This invention relates to a resiliently and pivotally mounted operator's cab for an earth moving vehicle or the like.
Operators' cabs on earth moving vehicles are often pivotally mounted to the frame of the vehicle to facilitate raising the cab from a substantially horizontal operating position in which it overlies the vehicle components to a tilted maintenance position in which the vehicle components are exposed for maintenance work and repairs. To obtain a sufficient amount of exposure of the vehicle components, it is often necessary to tilt the cab past an overcenter position in which the center of gravity of the cab is located directly over the pivot axis.
It is of the utmost importance that means be provided to prevent accidental free fall of the cab on either side of the overcenter position once it has been raised. Such free fall of the cab can, of course, cause extensive damage both to the cab and to the other parts of the vehicle. More importantly, free fall of the cab into its horizontal operating position could, of course, grievously injure maintenance personnel.
Proposed solutions to this problem have included the use of hydraulic lift cylinders or the like for raising and lowering the cab which employ various devices to prevent loss of hydraulic pressure and thus cab support. For instance, in U.S. Pat. No. 3,875,850 issued Apr. 8, 1975, to Reynolds et al, the practice of employing a velocity fuse to prevent uncontrolled free fall of a load in the event of a hydraulic fluid system failure is described. However, as noted in that patent, such fuses, although provided as a safety feature, may themselves be unduly exposed to possible failure unless integrally mounted within the hydraulic lift cylinder itself. In U.S. Pat. No. 3,578,377 of Babbitt, Jr., et al, issued Jan. 13, 1969, to the assignee of the present invention, a hydraulic cylinder is employed with a built-in, double-holding valve to prevent free fall of the supported load in either direction.
In addition to providing means to prevent free fall of the cab, it is desirable to resiliently mount the cab to the vehicle frame to isolate it against frame vibrations occurring during vehicle operation. The use of resilient bushing assemblies to achieve this objective is shown in U.S. Pat. No. 3,572,819 issued Mar. 30, 1971, to Moore et al, U.S. Pat. No. 3,527,474 issued Sept. 8, 1970, to Boersma, U.S. Pat. No. 3,036,858 issued May 29, 1962, to Fingerut and, most recently, in U.S. Pat. No. 3,847,492 of Kennicutt et al issued Nov. 12, 1974, to the assignee of the present invention. Resilient bushing assemblies of this type include a pair of mating connectors respectively secured to the cab housing and the frame, and a removable pin or bolt extending through the two connectors and supporting the overlying connector and the weight of the cab through a resilient bushing therearound.
A serious disadvantage of this type of mounting is that the weight of the operator cab supported by the pin substantially impedes removal of the pin to decouple the cab from the frame. This characteristic is particularly disadvantageous in those applications where the cab is pivotally mounted and intended to be periodically raised and lowered for repairs.